1. Field of the Invention
The present invention relates in general to a display scale for indicating the airspeed of a landing aircraft, and more particularly to a linear digitally activated display scale for displaying the airspeed and indicating the trend of the airspeed as either increasing or decreasing.
2. Description of the Prior Art
In the past, on aircraft carriers, at the Landing Signal Officer's (hereinafter LSO) control console, the technique for displaying airspeed was to use a synchro-indicator device for driving a pointer to indicate airspeed on a circular scale. The range of airspeed from 40 to 200 knots was far greater than required by the LSO. A range of 80 to 179 knots is adequate and will provide better resolution. The airspeed dial pointer did not indicate "changes" in the airspeed but only actual airspeed. Airspeed "changes", "decelerations" and "accelerations" as they are referred to by LSO's , are predictive of changes in glide-slope performance. Consequently, there is a need in the prior art to provide an airspeed display scale and associated equipment that will indicate both airspeed and airspeed change information, i.e., trend, to eliminate the circular dial and pointer systems which are difficult to read during some light levels of landing operations and to provide a linear scale with proper light level outputs.
In addition, one of the old techniques required the LSO to observe the airspeed scale for a longer interval of time in order to determine the trend of the airspeed, i.e., the trend could not be determined instantaneously. Another old technique required the assistant LSO to call out the airspeed readings and indicate as to whether each reading was increasing or decreasing. This technique, of course, had the added disadvantage of requiring the assistant LSO to make sure he was heard over aircraft noise and deck noise. Hence, there is a needed in the prior art to provide a linear display scale which is impervious to environmental noises and needs only one LSO for proper observation to properly operate.
Prior to the present invention, other techniques were investigated including the use of a servo-mechanism to drive a belt which carried a lit pointer along a linear scale. The foregoing technique and others using similar devices proved to have maintenance and mechanical limitations in terms of repeatability, stability and accuracy. Thus, there is a need in the prior art to furnish a linear digitally activated display scale which produces a continuous display of the airspeed and indicates the trend of the airspeed as either increasing or descreasing but yet be accurate and reliable.
The prior art as indicated hereinabove, include many advances in airspeed display scales. However, insofar as can be determined no prior art scale or indicator incorporates all of the features and advantages of the present invention.